Lecture 15 Nov. 1, 2013 Photosynthesis

8/13/2019 Lecture 15 Nov. 1, 2013 Photosynthesis

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Learning outcomes:

Sequencingenergytransformations

Linkinglight energy to

electrical energy to chemicalenergy

Recognizewhy photosynthesisis notthe reverse of cellularrespiration

Metabolism: PhotosynthesisLecture outline:

Photosynthesis

--light reactions

--synthetic reactions


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glucose

+

high potential energy

low potential energy

oxidation

C-H O-H

High potential energy low potential energy


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glucose

+



Photosynthesis: a whole lot

tougher for the cell

reduction

C-H O-H

High potential energy low potential energy


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1. carbons (source: CO2)

2. Electrons (H ) to make bonds (source: water H2O)

3. Energy (source: sunlight)


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"light reactions" = energy (sunlight ATP and electrons/reducing power

source of low potentialenergy electrons

source of high potential

energy electrons


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synthesis reactions"

(occurs in light and dark)

ordered

disordered


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thylakoid

membranesgrana

(photons)

Visible


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light excites electrons

to outer orbitals ofatoms




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Oneelectron transport chain is used to provide electrons

to make reducing power

=NADPH

electron "hole"

Electron transport chains

grab excited electrons

before they fall back to

original orbital.


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The first electron hole is filled with electrons excited

from a 2nd photosystem using 2ndelectron

transport chain (chain just like mitochondrial chain).

electron "hole" filled

here

NADPH

NAD+

ox

red

chain 1

chain 2

ATP


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Electron transport chain 2 works the same way as in the

mitochondrion: electrochemical gradients and ATP

formation


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The route of electrons: H20 to NADPH (and then

into sugars)

NADPH

NAD+

oxidized

reduced

ATP


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synthesis reactions"

(occurs in light and dark)

Th C l i l CO d i


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The Calvin cycle CO2 made in

respiration now added

to carbons in Calvin

cycle

Melvin Calvin

1961 Nobel Prize

Th C l i l


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The Calvin cycle

electrons, originally inwater, but now in

NADPH = reducing

power, create sugar.


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A re ie of photos nthesis


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A review of photosynthesis


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Photosynthesis: trace atoms from reactants to

products, as we did for respiration

+Genergy

electrons H

You do this trace for the easier pathway:

glycolysis + cellular respiration


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Neil Young

Someone in the audience yells out: "Itall sounds the same!"

Neil Young responds:

"Its all one song!"

Real quotes from the CD "Year of

the Horse" 1997


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C-H O-H

Be certain you can explain what makes a bond (and

participating electrons) high or low potential energy.

Lecture 2 should provide assistance.

Low potential energyHigh potential energy

Lecture 15 Nov. 1, 2013 Photosynthesis

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